802 Journal of the American Ceramic Sociery Kim and Kriven Vol. 87. No. 5 00 microns (b) Fig. 17. SEM microgrphs of the fracture surface of the three-layer fibrous monolithic composite 500 microns Fig. 18. SEM micrographs of the fracture surface of the mixed 50% two-layer: 50% three-layer fibrous monolithic composite. three-point bending strength of the composite was increased K. T. Faber and A. G. Evans, "Intragranular Crack However, the work of fracture of the composites did not show any Silicon Carbide, J. Am. Ceram. Soc., 66, C-94-C-96(1983). clear dependence on the composition of the composes d thre Evans, "Crack Deflection Processes-l. Theory,Acta Metall2,314]565-7601983) K. T. Faber, A.G. Evans, and M. D. Dory, "A Statistical layer mullite-AlPOa fibrous monolithic composites were fabri- cated. They exhibited apparent nonbrittle, intermediate, and brittle Mechanics of Ceramics, Vol. 6. Edited by R. C. Bradt, A. G D. P H fracture behaviors, respectively. The two-layer composite had the Hasselman, and FF. Lange. Plenum Press, New York, 1983 lowest three-point bending strength of 76 5 MPa and the highest N. Claussen, J, Steep, and R. F. Pabst, "Effects of Induced Microcracking on the work of fracture of 0.45+ 0.02 kJ/m. The two-layer mullite- A. G. E, gness of Ceramics,"Am Ceram. Soc. Bull, 56 [6]559-62(1977) ing of Ceramics by Circumferential AlPO4 fibrous monolithic composite showed evidence of exten- Microcracking, ". Am. Ceram. Soc., 64 [7] 394-98198 sive pullout and had a corresponding rough fracture surface. The .A. G. Evans, "Toughening Mechanisms in Zirconia Alloys' 193-212in reasons for this behavior were attributed to the formation of Advances in Ceramics, Vol. 12, Science and Technology of Zirconia /I Edited aussen, M. Ruhle, and A H. Heuer. American Ceramic Society, Columbus, OH, circumferential debonding cracks around the inner mullite rods sulting from differential sintering shrinkages between the porous M. Ruhle, N. Claussen, and A. H. Heuer, "Transformation and Microcrack AlPO interphase and the isolated inner mullite rods. The low level ing as Complementary Processes in ZrO2-Toughened Al2O3, " J Am Ceram. of pullout and brittle fracture of the three-layer fibrous monolithic so269115970196 of Fiber-Reinforced Ceramic Matrix composite were attributed to the formation of compressive stresses Cor in the AlPOa interphase layer, resulting from the high sintering Zok, Review: The Physics and Mechanics of shrinkage of the interconnected outer mullite layer. The fracture Fiber-Reinforced Brittle Matrix Composites, ". Mater. Sci., 29, 3857-96( 1994) urface of the mixed 50% two-layer: 50% three-layer fibrous Fiber-Reinforced Ceramics, ". Mech. Phys. Solids, 34, 167-89(1986). monolithic composite showed irregularly shaped pullout. nouless and A. G. Evans, " Effects of Pullout on the Mechanical perties of Ceramic-Matrix Composites, Acta Metall, 36, 517-22(1988) A. Curtin,"Theory of Mechanical Properties of Ceramic-Matrix 16W.J. Clegg. K. Kendall on, and J R. C. Garvie, R. H. J. Hannink, T. Pascoe."Ceramic Steel? Nature Simple Way to Make Tough Ceramics, Nature(London), 347[41455 17P. Boch, T. Chartier and M. H. Heuer, "Mechanisms of Toughening Partially Stabilized Composites,J. Am. Ceram Soc. Zirconia(PSZ),J.Am. Ceran. Soc., 60[3-4]183-84(1977) zhes, and D. S. Wilkinson, "Processing of H. Heuer, N. Claussen, W. M. Kriven, and M. Ruhle, "Stability of Tetragonal Tape Cast Laminates Prepared fror Alumina/Zirconia Powders, J.Anm Ceran ZrO2 Particles in Ceramic Matrices, J. Am. Ceram Soc., 65 [12]642-50(1982). Soc,778]2145-53(1994)three-point bending strength of the composite was increased. However, the work of fracture of the composites did not show any clear dependence on the composition of the composites. Two-layer, mixed 50% two-layer:50% three-layer, and three￾layer mullite–AlPO4 fibrous monolithic composites were fabri￾cated. They exhibited apparent nonbrittle, intermediate, and brittle fracture behaviors, respectively. The two-layer composite had the lowest three-point bending strength of 76  5 MPa and the highest work of fracture of 0.45  0.02 kJ/m2 . The two-layer mullite– AlPO4 fibrous monolithic composite showed evidence of exten￾sive pullout and had a corresponding rough fracture surface. The reasons for this behavior were attributed to the formation of circumferential debonding cracks around the inner mullite rods, resulting from differential sintering shrinkages between the porous AlPO4 interphase and the isolated inner mullite rods. The low level of pullout and brittle fracture of the three-layer fibrous monolithic composite were attributed to the formation of compressive stresses in the AlPO4 interphase layer, resulting from the high sintering shrinkage of the interconnected outer mullite layer. The fracture surface of the mixed 50% two-layer:50% three-layer fibrous monolithic composite showed irregularly shaped pullout. References 1 R. C. Garvie, R. H. J. Hannink, and R. T. Pascoe, “Ceramic Steel?,” Nature (London), 258, 703–704 (1975). 2 D. L. Porter and A. H. Heuer, “Mechanisms of Toughening Partially Stabilized Zirconia (PSZ),” J. Am. Ceram. Soc., 60 [3–4] 183–84 (1977). 3 A. H. Heuer, N. Claussen, W. M. Kriven, and M. Ru¨hle, “Stability of Tetragonal ZrO2 Particles in Ceramic Matrices,” J. Am. Ceram. Soc., 65 [12] 642–50 (1982). 4 K. T. Faber and A. G. Evans, “Intragranular Crack-Deflection Toughening in Silicon Carbide,” J. Am. Ceram. Soc., 66, C-94–C-96 (1983). 5 K. T. Faber and A. G. Evans, “Crack Deflection Processes–I. Theory,” Acta Metall., 31 [4] 565–76 (1983). 6 K. T. Faber, A. G. Evans, and M. D. Dory, “A Statistical Analysis of Crack Deflection as a Toughening Mechanism in Ceramic Materials”; pp. 77–91 in Fracture Mechanics of Ceramics, Vol. 6. Edited by R. C. Bradt, A. G. Evans, D. P. H. Hasselman, and F. F. Lange. Plenum Press, New York, 1983. 7 N. Claussen, J. Steep, and R. F. Pabst, “Effects of Induced Microcracking on the Fracture Toughness of Ceramics,” Am. Ceram. Soc. Bull., 56 [6] 559–62 (1977). 8 A. G. Evans and K. T. Faber, “Toughening of Ceramics by Circumferential Microcracking,” J. Am. Ceram. Soc., 64 [7] 394–98 (1981). 9 A. G. Evans, “Toughening Mechanisms in Zirconia Alloys”; pp. 193–212 in Advances in Ceramics, Vol. 12, Science and Technology of Zirconia II. Edited by N. Claussen, M. Ru¨hle, and A. H. Heuer. American Ceramic Society, Columbus, OH, 1984. 10M. Ru¨hle, N. Claussen, and A. H. Heuer, “Transformation and Microcrack Toughening as Complementary Processes in ZrO2-Toughened Al2O3,” J. Am. Ceram. Soc., 69 [3] 195–97 (1986). 11A. G. Evans, “The Mechanical Performance of Fiber-Reinforced Ceramic Matrix Composites,” Mater. Sci. Eng., A107, 227–39 (1989). 12A. G. Evans and F. W. Zok, “Review: The Physics and Mechanics of Fiber-Reinforced Brittle Matrix Composites,” J. Mater. Sci., 29, 3857–96 (1994). 13B. Budiansky, J. W. Hutchinson, and A. G. Evans, “Matrix Fracture in Fiber-Reinforced Ceramics,” J. Mech. Phys. Solids, 34, 167–89 (1986). 14M. D. Thouless and A. G. Evans, “Effects of Pullout on the Mechanical Properties of Ceramic-Matrix Composites,” Acta Metall., 36, 517–22 (1988). 15W. A. Curtin, “Theory of Mechanical Properties of Ceramic-Matrix Composi￾ties,” J. Am. Ceram. Soc., 74 [11] 2837–45 (1991). 16W. J. Clegg, K. Kendall, N. M. Alford, T. W. Button, and J. D. Birchall, “A Simple Way to Make Tough Ceramics,” Nature (London), 347 [4] 455–57 (1990). 17P. Boch, T. Chartier, and M. Huttepain, “Tape Casting of Al2O3/ZrO2 Laminated Composites,” J. Am. Ceram. Soc., 69 [8] C-191–C-192 (1986). 18K. P. Plucknett, C. H. Caceres, C. Hughes, and D. S. Wilkinson, “Processing of Tape Cast Laminates Prepared from Fine Alumina/Zirconia Powders,” J. Am. Ceram. Soc., 77 [8] 2145–53 (1994). Fig. 17. SEM microgrphs of the fracture surface of the three-layer fibrous monolithic composite. Fig. 18. SEM micrographs of the fracture surface of the mixed 50% two-layer:50% three-layer fibrous monolithic composite. 802 Journal of the American Ceramic Society—Kim and Kriven Vol. 87, No. 5